1. Technical Field
The present invention relates to a method of cleaning a plasma etching apparatus, and thus-cleanable plasma etching apparatus.
2. Related Art
With advance in generation of semiconductor devices, line pitch has been becoming narrower, and demands for dimensional accuracy in etching and other processes have been becoming more strict. Etching process has been proceeded by handling a plurality of wafers as one lot, wherein dimensional variation among the wafers has sometimes occurred with progress of pollution in a chamber of the etching apparatus. It is, therefore, a general practice to clean the inside of the chamber after the etching.
One of conventional plasma cleaning methods is such as described in Japanese Laid-Open Patent Publication No. H10-74732. The plasma cleaning method described in this publication is such as carrying out plasma cleaning, after completion of etching, using hydrogen chloride or a mixed gas of hydrogen chloride and chlorine, or hydrogen bromide or a mixed gas of hydrogen bromide and bromine as a cleaning gas.
Japanese Laid-Open Patent Publication No. 2004-235361 describes a method of manufacturing a semiconductor device, wherein in the process of etching a semiconductor wafer, the end point of dry etching is determined based on changes in intensity of plasma emission.
However, the conventional techniques described in the above publications still have a room for improvement.
First, the plasma cleaning method described in Japanese Laid-Open Patent Publication No. H10-74732 did not specify the end point of the cleaning. The method could therefore achieve only a limited degree of cleanliness of the inner wall of the chamber, and sometimes resulted in variation in line pitch among wafers in a single lot.
It has been a general situation that the conventional plasma cleaning was carried out for a constant duration of time, irrespective of the amount of deposit adhered on the inner wall of the chamber. The deposit might, therefore, remain adhered on the inner wall of the chamber even after the plasma cleaning, and might result in an insufficient cleanliness of the inner wall of the chamber. Moreover, the cleanliness of the inner wall of the chamber varied in the etching process repeated a plurality of times.
Relation between the cleanliness of the inner wall of the chamber and the variation in line pitch among wafers in a single lot is supposed as follows, although it is not completely clarified. More specifically, in the etching process, products derived from the etching gas adhere on the inner wall of the chamber and the wafer surface. Ratio of adhesion of the products ascribable to the etching gas between the inner wall of the chamber and the wafer varies, if the cleanliness of the inner wall of the chamber is insufficient in the succeeding cleaning process, and thereby the amount of deposition on the surface of wafer increases. For this reason, the variation in the line pitch is supposed to vary among wafers in a single lot.
Second, the method described in Japanese Laid-Open Patent Publication No. H10-74732 did not specify the end point of the cleaning, and sometimes resulted in an excessive cleaning time, thereby sometimes degrading the throughput.
In recent years, there has been an increasing trend of using an exposure apparatus using an ArF excimer laser (193 nm in wavelength) as a light source, aiming at achieving a fine line pitch. An ArF resist adaptive to the exposure apparatus is therefore used. The ArF resist has, however, a poor resistivity, needs etching proceeded under a low energy, and consequently needs a longer time for etching. Moreover, the conventional method never confirmed the end point of cleaning after the etching, and thereby occasionally resulted in an unnecessarily long time for the cleaning. As a consequence, the etching process as a whole including the cleaning process has sometimes been elongated, and has, in particular, resulted in degradation of the throughput.
As has been described in the above, there has been demands for a method of cleaning a plasma etching apparatus and a thus-cleanable plasma etching apparatus, capable of suppressing the variation in line pitch among wafers in a single lot, and of improving the throughput in the etching process.